Primary radar

A primary radar or primary surveillance radar (PSR) is a conventional radar sensor that illuminates a large portion of space with electromagnetic waves and detects the waves reflected back from targets within that space. The term thus refers to a radar system that can detect and localize potentially non-cooperative targets. It is specific to the field of air traffic control where it is distinguished from secondary radar which receives additional information from the target's transponder.

This type of radar uses a low vertical resolution antenna that has good horizontal resolution. It quickly scans 360 degrees around the site at a single elevation angle. It can thus give the distance and radial speed of the target with good precision but often requires one or more radars to obtain accurate vertical position and actual speed.

The advantages of the primary radar are that no equipment on-board the aircraft is necessary for detecting the target and it can be used to monitor the movement of vehicles on the ground. The disadvantages are that the target and altitude can not be identified directly. In addition, it requires powerful emissions which limits its scope.

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